In the field of road traffic which tends to increase every day, research has been carried out to facilitate as far as possible the flow of the traffic by establishing detours when the traffic undergoes a considerable slow down owing to the accumulation of vehicles on a highway or road section. The elimination of congestion requires knowledge of a certain number of data concerning the vehicles, their passage at a given location, their direction, their speed, etc.
All these items of information may be obtained from magnetic detectors which are disposed on alongside the road or embedded in the latter and which comprise at least one transmitting means, usually a coil, whose excitation creates a magnetic field around the detector, and receiving means such as a single or double coil or frame. A metallic mass, usually a vehicle, which is located in or enters the magnetic field created by the transmitting means disturbs the lines of force of the transmitted field.
This disturbance is detected by the receiving means and the information gathered therefrom is processed in associated electronic circuits.